Here's my 1990 Jimmy with a Con-fer roof rack mounted on the fiberglass top It was installed about 1 and a half years ago, and origrianlly I had my spare tire up there. But after about 6 months I noticed cracking inside the top... So I took the spare tire off...Thinking I could just leave the jack and (empty) gas can up there, and the top would be OK. Unfortunately this last weekend I was working on my truck (had the tailgate open for about 11 hours straight) and when I went to go close it...it wouldn't latch on the right side. It looks like the top is bowing out like this / \ Causing the bed reails to bow out like this \ / . As of right now, it has only happened on the right side. -That is nearly 3/4" seperation at the top of the bed rail / tail gate. below is the left side, not yet severely bowed... Some more top cracking... My Advice? DO NOT run a roof rack on your fiberglass top!